1. Field of the Invention
The invention relates to a circuit arrangement for generating rf signals for MR examinations, comprising a read-only memory in which a signal is stored in the form of a series of data words, an address generator for reading data words from the read-only memory with a clock frequency, and a digital-to-analog converter which succeeds the read-only memory.
2. Prior Art
Such a circuit arrangement is essentially known from the magazine "Neues aus der Technik", No. 1, Feb. 15, 1984, page 4, contribution 771. Circuit arrangements of this kind serve for generating rf pulses for MR examinations, for example for so-called MR tomography. During such examinations an rf oscillation is applied for some ms; the frequency, the phase or the amplitude of this rf oscillation may be modulated. The frequency of this oscillation is predetermined by the Larmor frequency which itself is determined by the flux density of the steady magnetic field generated in the MRI apparatus.
In the known circuit arrangement the variation of the complete rf pulse is stored in a fast digital memory. When it is constructed as a read-only memory such a memory must have a very high storage capacity, notably because a multitude of rf pulses having a different variation in time must be generated in an MRI apparatus.